1. Field of the Invention
The present invention generally relates to operational amplifiers and, more particularly, to an amplifier or integrator wherein offset, noise and long-term drift are auto-zeroed in a continuous way.
2. Description of the Prior Art
The requirement which led to the invention was the need to develop analog amplifiers and integrators that allow signal processing and offset cancellation without interruption of the signal path. Various approaches have been used in the past to provide continuous offset correction. The most well known is chopper stabilization which requires external components and has a significant recovery period if overloaded. A basic article describing this approach to stabilization is "Stabilization of Wide-Band Direct-Current Amplifiers for Zero and Gain" by Edwin A. Goldberg published in RCA Review, June 1950, at pages 296 to 300. Another approach is to store the error signal on a capacitor as described by John A. C. Bingham in "Applications of a Direct-Transfer SC Integrator" published in IEEE Trans. on Circuits and Systems, vol. CAS-31, No. 4, April 1984, at pages 419 and 420. However, in this latter approach, the signal path is interrupted during the offset sample period, which is a disadvantage in many applications.